1. Field of the Invention
The present invention relates to a steel-pipe sheet pile to be exemplarily employed in building a bridge foundation, and to a coupling structure of steel-pipe sheet piles.
2. Description of Related Art
It is presently essential to adopt a steel-pipe sheet pile foundation as one of bridge foundations. Upon building a foundation structure such as a pier within water, there are constructed cofferdam works based on steel-pipe sheet piles for coffering a targeted structure inside the cofferdam works.
As shown in FIG. 16 through 18, each of steel-pipe sheet piles 1 to be used for cofferdam works comprises a steel pipe 2 having right and left sides formed with joints 3, respectively, and the sheet piles are sequentially coupled to one another by connecting the pertinent joints 3 to the associated ones, respectively. Note that the mated joints 3 include various shape combinations such as: box shape and “T” shape; mutual “C” shapes; and “C” shape and “T” shape; and the illustrated ones are exemplary.
The steel-pipe sheet piles 1 are occasionally hammered by a hammering set machine (pile driver) based on a diesel pile hammer, which is accompanied by strong noise vibrations due to hammering operation, thereby leading to constructional pollution. Thus, there is also adopted a method for pressing sheet piles into the earth such as by a hydraulic jack or vibratory hammer while reducing an intrusive resistance by earth auger excavation, such that the steel pipes 2 are set-one by one as single elements in case of each of the hydraulic jack and vibratory hammer.
When the cofferdam works are constructed such as by inserting or hammering and placing the steel pipes 2 one by one into excavated holes in the above manner, there are required considerable time and effort and the joints 3 tend to be bent due to increased inserting resistances upon constructing the cofferdam works, thereby making it difficult to ensure the vertical precision of the steel-pipe sheet piles 1 themselves.
Although it is possible to simultaneously establish a plurality of excavated holes by employing a multi-auger machine as the earth auger in case of setting the steel-pipe sheet piles 1 into excavated holes provided by the preceded earth auger excavation in the above manner, the man-hours are not reduced because the steel-pipe sheet piles 1 are arranged principally one by one in the above manner.
Further, it is assumed to be technically difficult to perform the above construction method, about water depths exceeding 10 meters in case of a soft ground and about water depths exceeding 15 meters in case of a hard ground. Particularly, there has been issued such an administrative notification that the construction method based on a single steel-pipe sheet pile should not be adopted in deep water, in view of the defect due to the insufficient water-stopping ability of the construction method.
Meanwhile, the portions of joints 3 are exerted with shearing forces in the up-and-down direction, when the steel-pipe sheet pile foundation is exerted with external forces in a horizontal direction. Shearing forces stronger than shearing yield strengths of the joints rapidly increase shearing deformations of the joint portions, thereby also considerably deteriorating the bending rigidity of the whole of the steel-pipe sheet pile foundation.
To overcome such disadvantages, there has been provided a steel-pipe sheet pile, which is capable of achieving a larger strength of the whole of the steel-pipe sheet pile than the conventional, such that multiple steel pipes can be simultaneously hammered and placed to thereby remarkably shorten the constructing term, and multiple steel pipes are previously coupled to one another with a predetermined precision to thereby attain a higher constructing precision and an improved vertical precision (see Japanese Patent Application No. 2001-7198112 (JP-A-2003-13441)).
The technique noted just above is to hammer and place combined bodies of previously and integrally coupled multiple steel-pipe sheet piles as shown in FIG. 19, in which two juxtaposed steel pipes 2, 2 are integrally coupled to each other by an H-shaped steel-beam 4 acting as a tying member of an H-shaped transverse cross-section and having flange edges coupled to the peripheral surfaces of the associated steel pipes 2, respectively, while providing joints 3 at sides of the steel pipes opposite to the mutually coupled sides, respectively.
This H-shaped steel-beam 4 may be an extrusion molded one, or independently and appropriately assembled by welding such as in a factory. In case of employing the shaped steel-beams, right and left edges of flanges 4a are to be welded to the peripheral surfaces of the steel pipes, thereby defining a tightly closed space 5 enclosed in all directions by these parallel flanges 4a and steel pipes 2, 2. In this figure, reference numeral 4b designates a web.
The steel-pipe sheet pile 1 is established into a double-pipe type, based on the joints 3 provided at sides of the steel pipes 2, 2 opposite to the mutually coupled sides by the H-shaped steel-beam 4, respectively. The joints 3 are similar to those conventional ones shown in FIGS. 16 through 18, and these exemplary configurations are the same as those of FIG. 17, i.e., each steel pipe 2 is weldedly mounted at its peripheral surface with a tube body of a C-shaped transverse cross-section, which is an annular body having a slit 3a. Although the joint 3 itself is provided on the steel pipe 2 strictly in the transverse direction of the associated steel pipes 2, the slit 3a is opened not in such a transverse direction but in an oblique direction, so that slits 3a are opened in symmetrical directions when the joints 3 are opposed to each other, resulting in that the joints 3 are engaged with each other in a manner that the joints 3 enter each other through slits 3a, respectively.
Note that the joints 3 are not limited to the shown examples, and it is possible to adopt as another example such simple shapes that one of the paired joints is a single male member to be inserted into a spacing defined by two pieces of the other female member.
Each steel pipe 2 is mounted with a tube body 17 having a slit 17a such as by welding at the peripheral surface of the steel pipe near the associated joint 3, so as to protrudingly provide an engagement groove 6 outside the steel pipe 2. The slits 17a of these tube bodies 17 are opened in oblique directions, respectively, such that those lines drawn from these openings are interconnected with each other to define an arc when the joint 3 of one sheet pile is engaged with that of another sheet pile. Note that each tube body 17 has a diameter smaller than that of the joint 3.
In this figure, reference numeral 18 designates a flexible plate such as made of steel plate having flexibility and having opposite ends provided with pipes 19 as anchoring members, respectively, such that these pipes 19 are allowed to be inserted into the tube bodies 17 constituting the engagement grooves 6, respectively.
According to this Japanese Patent Application No. 2001-7198112, each steel-pipe sheet pile defines a tightly closed space enclosed in all directions by the shaped steel-beam and the steel pipes. Namely, the steel-pipe sheet pile is in the shape including the steel pipes and the H-shaped steel-beam welded at four ends to the steel pipes in a manner to establish an integrated jointed-steel-pipe sheet pile comprising multiple steel pipes joined to each other by H-shaped steel-beams, thereby enabling a correspondingly increased strength and allowing support of loads not only in the minor axis direction but also in the major axis direction.
This simply reduces the number of couplings between the joints down to a half or less, of the number of conventionally constructed joints, and also reduces the number of water stopping works (such as mortar impregnation or chemical grouting), thereby achieving a (environment protecting) construction which has an improved economical effect and which is friendly to the environment based on the reduced contamination of water quality by virtue of the reduced-impregnation amount. Further, varying the shapes of the coupling H-shaped steel-beams enables construction of shaped portions having every possible curvature.
Simultaneously hammering and placing two steel pipes is more advantageous than hammering and placing one by one and enables a remarkably shortened constructing term, so that the remarkably shortened term of pontoon usage such as seen in a marine construction exhibits an economically greater advantage as even compared with a land-based construction. Further, two steel pipes are joined to each other at a predetermined precision, thereby providing a higher constructing precision and improving a vertical precision.
Moreover, the configurations joined by the H-shaped steel-beam members can be effectively utilized in a manner to reduce the time and laborious efforts for exemplarily boring holes in conventional steel pipes such as in construction and installation of back anchoring tie-rods, thereby achieving an economical advantage.
Coupling by the H-shaped steel-beams enables the surface of each of the hammered and placed steel pipes in the minor axis direction to be readily reinforced and coupled, thereby allowing utilization and development in “inhibiting pile”, “landing pier” and “temporary bridge” by utilizing such characteristics that the coupled steel pipes provide not only a bending rigidity in the minor axis direction but also a higher bending rigidity in the major axis direction.
Moreover, the exterior portions of the joints are enclosed by the flexible plate to thereby attain water stopping at these portions, such that the flexible plate can be installed in an extremely simple manner to insert the anchoring members at the ends of the flexible plate into the engagement grooves, respectively. Note that the flexibility of the flexible plate allows it to be curved and bulged, thereby facilitating dimensional adjustment.
While the steel-pipe sheet pile described in the Japanese Patent Application No. 2001-7198112 exhibits the shape where one steel pipe is welded to the other steel pipe at four ends of the H-shaped steel-beam in a manner to already ensure a sufficient rigid ability by virtue of the jointed-steel-pipe sheet pile comprising multiple steel pipes joined to each other by the H-shaped steel-beam so that a further rigid ability appears to be unnecessary, the rigidity should not be considered for the coupling between the joints of such conventional jointed-steel-pipe sheet piles themselves each having joints at opposite ends, from a designing standpoint.
Then, the portions of the joints 3 are exerted with shearing forces in the up-and-down direction when the foundation formed of the steel-pipe sheet piles is exerted with external forces in a horizontal direction. Shearing forces stronger than shearing yield strengths of the joints rapidly increase shearing deformations of the joint portions, thereby also considerably deteriorating the bending rigidity of the whole of the steel-pipe sheet pile foundation.
Methods for improving the shearing yield strength of the joint itself include: a method for providing many projections at an inner surface of a circular steel pipe constituting the joint member to thereby improve the shearing yield strength of the joint by enhancing a bonding strength between the circular steel-pipe and the mortar by virtue of the effect of the projections; a method for increasing the diameter of a circular steel pipe constituting a joint member to thereby improve the shearing yield strength of the joint by increasing a bonding area between the circular steel pipe and mortar by virtue of the increased diameter; and a method as shown in JP-A-2000-220135, which provides bumps on an inner surface of a circular steel pipe as a joint, and which provides a reinforcing member for coupling an outer surface of a main pipe to an outer surface of a circular steel pipe at a longer arc of two arcs of the circular steel pipe, the two arcs circumferentially extending: from a mounting portion of the circular steel pipe to the main pipe of the steel-pipe sheet pile; to a position of a slit of the circular steel pipe.
However, the strength of the joints have not been sufficient, even by such techniques.
Moreover, in case of continuously hammering and placing the conventional jointed-steel-pipe sheet piles each having joints at opposite ends, respectively, the jointed-steel-pipe sheet piles themselves are joined to each other by the conventional joints (such as P—P joint). Thus, although the perfect water stopping can be achieved for each jointed-steel-pipe sheet pile in itself, there remains a risk of water leakage at the location between the conventional types of joints of the jointed-steel-pipe sheet piles. Therefore, it is an essential theme to improve the water-shielding ability at the locations of joints at opposite ends of jointed-steel-pipe sheet piles, in case of utilizing such sheet piles as a revetment for a waste landfill.
It is therefore an object of the present invention to provide a steel-pipe sheet pile and a coupling structure of steel-pipe sheet piles, capable of overcoming the disadvantages of the aforementioned conventional examples and capable of improving both of rigid ability and water-stopping ability at a gap between joints not only in steel-pipe sheet piles each comprising a single steel pipe provided at opposite peripheral sides thereof with joints, respectively, but also in a double-pipe type of steel-pipe sheet pile.